Method of forming metallic oxide coatings upon siliceous support articles



Dec. 18, 1951 A. R. WEINRICH N I Ms 0 m EI ET m m T9 CR1 um m MSW cw N MW Ic mu OIF FS F D n mU m M H65. H61 no.4.

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All/AV 1 1 1 1 1 1 11 1111 1 1 11 1 11111 1111/1/1//1/1fl// O 6 INVENTOR. ARTHUR R.WE|NR|CH M W ATTO RN EYS Patented Dec. 18, 1951 METHOD OF FORMING METALLIC OXIDE COATINGS UPON SILICEOUS SUPPORT ARTICLES Arthur R. Weinrich, Brackenridge, Pa., assignor to Libbey-Owens-Ford Glass Company, Toledo, Ohio, a corporation of Ohio Application November 3, 1947, Serial No. 783,841

16 Claims.

This invention has to do with a method of forming metallic oxide coatings upon siliceous support articles.

Thermally evaporatedcoatings of certain metallic oxides deposited upon glass or other siliceous supports by evaporation in a vacuum have i been found to be of interest by reason of their optical characteristics, their hardness, and their stable nature as mirror reflective coatings, as coatings in low reflection coated articles, as durable protective coatings upon such articles, and in various other articles and uses as coatings. In such articles the use of the highly oxidized solid metallic oxide coatings of aluminum trioxide, titanium dioxide, chromium sesquioxide, tin dioxide, zirconium dioxide, and antimony tetraoxide is particularly desirable and for certain uses coatings of the similar higher oxides ferric trioxide, tantalum pentaoxide, tungsten trioxide, manganese oxide, and the aluminum oxide spinels are attractive. Each of these metallic oxides is the higher oxide of the metal in each case which is stable under atmospheric conditions and excepting the chromium and manganese oxides are generally colorless or of light color. However, when coatings of these materials are formed by thermal evaporation of the substances in a vacuum the coatings thereby produced are darker than would be expected and are found to absorb considerable light and further the reflective properties and their activit in low reflection coatings in combination with other layers is not what would be expected based upon their normally given refractive indices.

At the same time, deposition by thermal evaporation is very desirable by reason of the accuracy and fineness of control possible in depositing extremely thin, uniform, continuous coatings. Furthermore, in the production of a highly oxidized metallic film, the deposition by thermal evaporation of a metal oxide is preferable to the initial deposition of a metal, followed by oxidation. Metals tend to short out on the filament, giving rise to variable temperatures and non-uniform conditions. This is not true of the oxides and thus accurately controllable conditions can be attained. In addition, some metals while man of the simple lower oxidized metallic oxides such as zinc oxide, beryllium oxide, sodium oxide, ferrous oxide, or titanium monoxide may be thermally evaporated in a vacuum without decomposition and loss of the oxygen, the higher oxygen-containing or more highly oxidized solid metallic oxides above described while stable when heated in air are unstable in a vacuum when heated and thermally evaporated losing some oxygen and the coatings then deposited upon the article to be coated by thermal evaporation are formed either primarily or to some degree of some lower oxide of these metals and these lower oxides are generally of a dark color and the coatings are thus caused to absorb considerable light. As such lower oxides are of considerably different refractive index than the refractive index of the desired higher oxidized metallic oxides the optical reflection activity of the coatings either in a mirror or a low reflection coated article are thus different from that desired in the coatings. Thus thermal evaporation of yellow or black titanium monoxide or of the green black titanium sesquioxide or of the colorless white titanium dioxide gives coatings which at the same thicknesses are of about the same reflection and light transmission characteristics. Oxygen is lost from the two higher oxides during the thermal evaporation as may be noted from the vacuum gauges indicating the vacuum becoming poorer during the thermal evaporation as gas is generated as the oxides evaporate and partially decompose. On the other hand, as soon as the deposits begin to form there immediately follows an improvement in the vacuum as the oxygen is again absorbed to some degree by a partial recombination of the lower oxides in the deposit with oxygen. It would thus seem that in all three cases the coatings secured by thermal evaporation of the different titanium oxides were largely formed of a mixture of titanium oxides including some of the lower oxides and probably titanium monoxide. In a similar manner, thermal evaporation in a vacuum of ferrous oxide (FeO) or of ferric trioxide (F9203) seems to give the same type of coatings which appear to be mainly ferrous oxide as loss of oxygen from the ferric trioxide is evidenced by the vacuum gauge reading variation when the latter material is evaporated thermally in a vacuum.

When coatings upon glass or other vitreous siliceous support articles such as porcelain, tile, ceramic, earthenware, aluminum silicate, calcium silicate, mica, or silica which are heat resistant bodies, are first formed by thermal evaporation in a vacuum by the evaporation of either one of the lower metallic oxides, such for example as titanium monoxide, or of one of the higher metallic oxides listed in the first paradegree of light absorption. I have found that 6 .1 graph, such as titanium dioxide for example, I

have found that the undesired or high light absorbing deposit thus secured may be changed into the desired less light absorptive coating of the higher more highly oxidized solid metallic oxide substantially or completely by heating the coated support surface in an oven or furnace in contact with air, oxygen, or an oxygen-containing atmosphere at temperatures of above 100 centigrade up to a temperature just below the melting point of the support article, such as 800 centigrade. The coating of lower oxide or of mixed oxides containing some lower oxide is thus oxidized to a coating of the more desired highly oxidized solid metallic oxide which is stable under such conditions of heating in air or the presence of oxygen.

In general then the invention comprises the method of forming coatings and preferably partially transparent coatings of a desired minimum light absorption upon the surface of a vitreous siliceous support article such as glass, silica, or the like, in which a coating is first deposited upon such support by the thermal evaporation within a vacuum from a heat radiating support body of a metallic oxide which is thereby heated, the metallic oxide being an oxide of a metal which is characterized by forming metallic oxides of several diiferent states of oxidation or oxygen content such as any of the oxides of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten, manganese, or mixtures of any of these together or in chemical combination with other metallic oxides such as alumi-- num oxide with other metallic oxides in the spinels and thereafter'subjecting the coated support article and deposit, which deposit will include therein a metallic oxide of low oxidation state, to a heating in an oxygen-containing atmosphere at a temperature in excess of 100 centigrade and below the melting or softening point of the support to oxidize the deposit to form the desired coating or partially transparent coating upon the article, the coating thus produced being composed substantially of the normal stable highly oxidized solid metallic oxide which with the respective metallic oxides listed would be aluminum trioxide, titanium dioxide, chromium sesquioxide, tin dioxide, zirconium dioxide, antimony tetraoxide (Sb204) or antimony pentaoxide (SbzOs), ferric trioxide, tantalum pentaoxide, tungsten trioxide, manganese sesquioxide (MnzOa) or manganous manganic oxide (M11304) mixtures of these highly oxidized metallic oxides together or in combination with other metallic oxides in spinels, such, for example, as aluminum trioxide with other metallic oxides. Further examples of the spinels which may be looked upon as combination of metallic oxides may be found at pages 687-712 in Danas System of Mineralogy, Seventh Edition, published in 1946 by John Wiley 8: Sons, such for example as spinel (MgOA12O3), Franklinite (ZnOFezO3), and chromite (FeO-Crzs).

The higher oxides of the specified metals, possibly by reason of their higher oxygen content, are generally of lower refractive index and almost invariably of lighter colors than the lower oxides of the same metals. In thin coatings the lower oxides of deeper colors are thus more light absorptive and the presence of such in the metallic oxide coatings as secured by direct thermal evaporation in a high vacuum is thus objectionable. By my invention the desired coatings of the more highly oxidized metallic oxides which are of generally low light absorption are thus SQQ J' IQQ.

substantially, free of the undesired lower oxides. It will be apparent that where several higher oxides of a metal can be formed upon heating the metal oxides in air or oxygen containing atmosphere that appropriate heating at suitable temperatures and pressures will be employed to secure a coating of the desired oxide. As will appear later, the alternative forming of a deposit of antimony pentaoxide or of antimony tetraoxide may be accomplished by the thermal evaporation of an antimony oxide material and the heating of the deposit in air thereafter by a suitable choice of temperature and pressure at which one or the other of these higher oxides of antimony are normally formed and stable. Similarly, while manganese is known to form several higher unstable oxides such as M11207 which is an unstable oil, MnOa and MnOz which are decomposed also by heating in air and a low oxide MnO it is apparent that when I heat my manganese oxide deposits secured by thermal evapo ration of a manganese oxide I will not form any of these higher unstable oxides of manganese and that I will oxidize any managanous oxide MnO, etc., in my deposits to one of the normally stable higher oxides of manganese which are manganese sesquioxide or manganous manganic oxide. The product secured in this case will be the sesquioxide as a coating if the oxidation is carried out in oxygen and with air oxidation will be the manganous manganic oxide. The choice of heating conditions may thus be used to ar rive at a choice of various higher oxidized metallic oxide coatings in some cases. Obviously by raising the temperature during the oxidation heating I may accomplish the desired oxidation in the deposit to secure my desired coating in a. shorter time or I may if preferred carry the step out at a lower temperature for a much longer time. As the coating thickness which is treated during the oxidation heating is increased the length of time of treatment may be increased and the temperature of treatment may be increased to secure the desired substantial conver-- sion of the lower oxides in the thermal1yevaporated deposit to the higher oxidized metallic oxides. If desired I may also accelerate the oxidation of the deposit to the desired oxidized coating by also employing the oxygen, air or other oxygen containing atmosphere at pressures somewhat greater than atmospheric and it will also be apparent that the oxygen containing atmosphere may be used in the oxidation at pressures somewhat less than atmospheric but ordinarily not less than 50 millimeters partial pressure of oxygen.

It is an object of this invention to provide a method for producing coatings of the higher metallic oxides upon supports by thermal evaporation.

It is a further object of the invention to provide a method for forming coatings of the higher metallic oxides which are substantially such and partially transparent and of a minimum light absorption.

As another object of the invention the method of forming coatings upon smooth transparent supports of the higher metallic oxides is shown as. a means of thereby producing partially trans-- parent mirrors.

As a further object the method is provided for the coating of mirror reflective surfaces upon suitable supports for the forming of mirrorarticles having a protective face thereon of a coat-- ing of a higher metallic oxide which is desirably" of minimum light absorption and partially transparent.

The process applies the advantages of thermal evaporation of materials in a high vacuum to secure even, uniform, continuous coatings and by the oxidation step overcomes the difficulties of high light absorption and the presence of undesirably large amounts of lower metallic oxides in such coatings when the metallic oxides are thus applied. The various advantages and uses of the process will be more apparent from the following examples which are illustrative but not limiting thereby.

By way of indicating how I may proceed with the compounds known as spinels or with mixtures of metallic oxides I may evaporate within a vacuum a magnesium spinel which consists of magnesium oxide in combination with a molecule of aluminum trioxide or may directly evaporate a simple intimate mixture of molecular equivalent quantities of powdered magnesium oxide and powdered aluminum trioxide and in either case the deposited coating will be found to become less light absorptive upon heating the support carrying the deposit at 100 centigrade in air. In each case the dark lower oxide of aluminum present in the deposit first formed by thermal evaporation in the vacuum, which is presumed to be aluminum monoxide (A16), is thereby oxidized to the colorless aluminum trioxide (A1203) and the spinel is then reformed in the coating thus secured by re action in the heated deposit with the magnesium oxide.

Dark monoxides of the metals seem to be formed to some degree as many of the higher metallic oxides are thermally evaporated and appear to be the source of the undesirable light absorption in the deposits thus secured directly. Thus aluminum monoxide (A) is a very deep black substance. the product titanium monoxide (T10) is a deep black substance or a yellow substance, chromium monoxide (CrOl is also black, stannous oxide (SnO) is black, ferrous oxide (FeQ) is a dark black green, and the manganous oxide (M110) is a dark green black. Possibly other dark monoxides of some of the other metals exist. All such ox des oxidize easily when heated as suggested hereafter.

Figure 1 shows in section a suitable thermal evaporation apparatus or vacuum chamber for carrying out the process having therein suitable evaporation elements which may be electrically heated to cause evaporation of materials placed thereon.

F gure 2 shows a suitable evaporation filament which may be of tungsten or tantalum and which carries thereon a metallic oxide for evaporation or a metallic compound which when heated will form a metallic oxide.

Figure 3 shows another suitable form of evaporation element comprising a boat of tungsten, tantalum or molybdenum, which has therein a suitable intimate mixture of metallic oxides for thermal evaporation of the mixture.

Figure 4 shows a plate after it has been processed in accord with the invention by heating an oxide deposit in contact with an oxygen containing atmosphere at an elevated temperature and carrying thereon a solid coating thus produced which is substantially higher metallic oxide in a continuous layer.

Figure 5 shows a metallic mirror after it has been processed in accord with the invention by heating an oxide deposit in contact with an oxygen containing atmosphere at an elevated temperature and carrying upon the unaltered reflective layer a coating thus produced of a solid highly oxidized metallic oxide.

Figure 6 shows a ceramic bowl, partly in section, having thereon a coating produced in accord with the invention of a highly oxidized metallic oxide which gives the bowl a protection. from wear and a high reflection or luster.

Figure '7 is a transverse section through a plate provided with a plurality of coatings, one or more of which are produced in accordance with the present invention.

Referring now to the drawings, there is shown in Figure 1 a suitable apparatus for carrying out the present invention. Mounted upon a plate I 0 and in sealed relation therewith is a bell or chamber I I within which a vacuum is maintained. At I2 there is indicated a connection t a suitable vacuumpump (not shown) for evacuating the interior of the bell I I. Within the vacuum in the bell and herein illustrated as carried by the plate I!) is a support I3 adapted to support an article M. The article I4 may conveniently be a plate of vitreous siliceous material, such for example as glass.

Within the vacuum chamber II are a pair of heating filaments I5 and I6 carried by supports I1 and I8, respectively. Intermediate the filaments l5 and I6 there is illustrated a plate or shield I9 movable between the full and dotted line positions shown and adapted to be moved between such positions by an actuating element 20. A well 2| is provided to permit downward movement of the shield I9 to a position where it permits deposit by thermal evaporation upon the surface of the element I4 from material contained within the filament H5.

The apparatus illustrated is effective to carry out the first step of the herein disclosed method. Thus, for example, an oxygen containing metal compound such as indicated at 22 may be located within the filament I5 and heated thereby to effect deposit of metallic oxide, including a lower oxide, on the exposed surface of the element I4. Following deposition of the metallic oxide on the surface of the element I4, the second step of the operation is carried out by heating the surface of the element I4 in an oxygen containing atmosphere to oxidize the lower metallic oxide or oxides to the desired higher metallic oxide.

The apparatus illustrated in Figure 1 may be used to produce an article having a surface thereof provided with two dissimilar coatings, the outer one of which may be the highly oxidized metallic oxide coating disclosed herein. Thus, for example, the article I4, which may be a plate of glass, may have deposited thereon by thermal evaporation from thefilament [5 a reflective mirror coating. At this time the shield 19 may be in the full line position which prevents deposition of thermally evaporated material onto the filament I6 from the filament I5. After the desired mirror coating has been deposited upon the surface of the article I4, the filament I5 is deenergized, the shield I9 is moved away from its shielding position intermediate the filaments I5 and I6, andthe filament I6 which contains the desired material for depositing metallic oxide may be energized. Thus the metallic oxide is deposited directly upon the reflective mirror coating. In any event, after deposition of the metallic oxide coating the article I4 is heated in an oxygen containing atmosphere and preferably by means of a flame or in an electric oven under atmospheric pressure so as to oxidize the lower metallic oxides to the desired higher metallic oxide.

In Figure 2 there is illustrated apparatus suitable for effecting thermal evaporation of the me tallic oxide, metallic compound or the like. In this figure there is illustrated a coiled filament 36 which may be formed of tungsten, tantalum or the like and which is adapted to support pieces 3| of the material to be evaporated. Energization of the filament 30 results in heating the pieces 3| to a high temperature with the result that a metallic oxide or metallic oxides are evaporated. The filaments l5 and I6 illustrated in Figure 1 may be identical with the filament 38 illustrated in Figure 2.

Referring now to Figure 3, there is illustrated an evaporation element comprising a boat All which may be formed of tungsten, tantalum or molybdenum. The boat 40 is provided with conductors M and 42 by means of which current is supplied thereto. The material to be evaporated by thermal evaporation is placed within the boat 40 and in this case the evaporated metallic oxide is evolved upwardly. In the figure there is illustrated at 43 an article to be coated by thermal evaporation and it is shown in position directly above the boat l!) in best position to receive metallic oxide deposit therefrom.

Referring now to Figure 4, there is illustrated an article in the form of a plate 50 provided with the coating 5i of metal oxide. This article results from deposition by thermal evaporation such as, for example, produced by the apparatus illustrated in Figure 1, employing a filament such as that shown at 30 in Figure 2, a boat such as that shown at 40 in Figure 3 or other means.

In Figure 5 there is illustrated a reflective mirror produced in accordance with the present invention. In this case the support article 60 is in I the form of a smooth surfaced plate to which is applied a reflective mirror film 6| which may if desired be of metal. Overlying the reflective mirror film 6 is the metallic oxide film 62 produced in accordance with the method disclosed :1

herein. In this case the mirror illustrated is preferably -a first surface mirror and the provision of the metallic oxide coating 62 protects the reflective mirror coating 6|. At the same time due to the relatively low light absorption resulting from the oxidation of lower metallic oxides to the desired higher metallic oxides the eiiiciency of the mirror is not appreciably reduced by the protective coating applied thereto.

Referring now to Figure 6, there is illustrated a ceramic bowl 10, a portion of which is broken away to illustrate the relationship of parts. The metallic oxide coating 1! is illustrated as applied to the exterior of the bowl so that it protects the bowl from wear and may impart thereto a high reflection or luster.

Figure 7 shows an article 86 to which three successive coatings BI, 82 and 83 of solid highly oxidized metallic oxide have been applied by separate retreatment or preferably by the successive thicknesses of each of the coatings, articles of high or low reflection properties may be obtained.

Obviously one or more of the coatings may be of other transparent materials such as metallic monoxides of fluorides which are stable under the oxidizing treatment and not thereby altered. Thus, for example, the intermediate layer 82 in Figure '7 may be beryllium oxide (BeO) or magnesium fluoride (MgFz) while layers 8! and 83 may be any of the higher metallic oxides described herein.

While specific apparatus has been illustrated for carrying out the initial step of deposition by thermal evaporatiomthe apparatus for carrying out the second step has not been illustrated. The second step involves the heating of the coated surface in an oxygen containing atmosphere which may be accomplished as previously stated by flame, an electric furnace or the like. Preferably, however, the final heating step to produce the desired highly oxidized metallic oxides is carried out at atmospheric pressure. One reason for this is that certain of the higher metallic oxides which are stable under atmospheric pressure, will be unstable when heated within a vacuum.

EXAMPLES 1 TO 4 Four pieces of cleaned plate glass were placed within a vacuum chamber with a smooth surface of the glass facing a tungsten coil filament containing 0.200 gram of aluminum trioxide pieces. Two ofv the sheets of such glass supports were placed 14 inches away from the filament and two were placed at 22 inches away to secure a lighter coating. The chamber was then closed and the plates were then given a glow discharge cleaning in a poor vacuum and thereafter the Vacuum was further improved to about 10- mm. Hg pressure or lower and the coil containing the aluminum trioxide was then heated electrically to a high temperature to supply heat by radiation and direct contact to the aluminum trioxide and to cause it to evaporate. As the evaporation started there was noted upon the vacuum gauges attached to the vacuum chamber the development of a surge of gas as oxygen was liberated from the heated oxide and thereafter the vacuum again improved somewhat as oxygen was absorbed to some degree by the deposit being formed upon the glasses. When the coated glasses were removed from the vacuum chamber the coatings were clear, non-metallic, and evidently composed of aluminum oxides. Measurements of the refiection and light transmission characteristics were then made and one of each set of the glasses was then subjected to oxidation by heating the coating directly by applying a Bunsen burner gas flame directly upon the coating in the air. As will be seen from the following table of measurements the reflectivity and transmission measurements changed indicating that some lower oxide of aluminum present in the deposited coating was thus oxidized and changed into the highly oxidized aluminum trioxide. The changes were greater and the oxidation substantially complete when the other two coated glasses were heated in air in an electric oven at 370 centigrade for 15 minutes as appears in the table. In each case the oxidation of the coating will be seen to have reduced the light absorption of the coatings as the less light absorptive colorless aluminum trioxide was thus formed from the lower oxides of aluminum present in the coating with aluminum trioxide. Aluminum monoxide is a dark brown black light absorbing substance. The coatings thus produced were hard 9 and weather resistant and the coated glasses could be used directly as partially transparent mirrors. The coatings thus applied to the glass plates could also by the further application of other coatings thereupon of transparent mate- 10 the spinel from the heated tungsten coil at a vacuum of about 10- millimeters. As the evaporation started there was noted upon the vacuum gauges attached to the vacuum chamber the development of a surge of gas as oxygen was liber- 5 rials of different refractive index be built up into ated from the heated material and thereafter a low reflection coated glass article in Ways the vacuum again improved somewhat as oxygen known to the art, the reduced light absorption was absorbed to some degree by the deposit being character of the aluminum trioxide coating thus formed upon the glasses. The spinel evaporates produced being highly desirable for such applicompletely so that the magnesium oxide content cations, thereof as well as various aluminum oxides were As the refractive index of aluminum trioxide evidently present in the clear coatings found is 1.77 and an optical thickness of coating of a up n he glass sheets wh n y W r r m ve quarter wave length factor is determined b difrom the chamber. Measurements of the li h viding the wave length of light (A) by 4 and also reflection I and transmission and absorption of by the refractive index (N) of the coating it will the coated pieces were made directly on the coatbe seen that the coatings of Examples 3 and 4 ed glaSS Supports and also upon sets of these were thu on quarter of a wave l n th thick glasses which were in one case directly oxidized with respect to visible light of 5500 Angstrom 11 air y th app e t n f an u n tin ga units. As color is developed by light interference P fl d c y tn the coating urface and in the reflected light when the coating thickness In a Second S Which e OXidiZed y p is a whole odd integer number such as 1, 3, 5, 7 or the Po d g se in an electric oven at 370 9 times the quarter ave factor centigrade IR?! 15 minutes. The measurements A in the following table show that the oxidation of m the coatingsgave final coatings of decreased light Q absorption and of changed light reflection and and the wave length is one occurring in visible light transmission characteristics. The heating light of 4000 to 7500 Angstrom units wave length and oxidation of the coatings would thus seem to it is apparent that the partially transparent mirhave oxidized any lower oxides of aluminum presrors produced as Examples 3 and 4 are also colcut in the coatings and to have caused a reaction cred mirrors and each was found to have a red between the aluminum trioxide formed by the purple red color by reflection. oxidation or directly present with the magnesium Aluminum trioxide coatings Per Cent Per Cent 1 0t 0 t PerGet ag t tt ut? his. Stir; t. ches Microns mission Reflection Absorption 1 22 88 11 1 22 .031 88.5 10.5 1 2 22 as 11 1 22 .031 90 1o 0 s 14 78 17.4 4.0 14 .070 79 17.4 3.0 4 14 78 17.4 4.0 14 .076 Oven 80 16.8 3.2

When the specimen of Example 4 was further oxide present to form a coating of the spinel or heated in an oven at 425 centigrade for one hour, magnesium aluminate. The coatings were very light absorption was reduced to 0%. hard and durable and suitable for use in forming Spinal coated glass sheets P o t P o Exfimple gggg i g ggg Oxidation l figlft %ro1i? eriggit Inches Microns Step 2 i gg g Absorption 84 14.2 1.12 e as 14 3 as 12 o 7 73 15 12 EXAMPLES 5 TO 8 In a similar manner to the preceding examples, four plates of clear clean glass were coated by evaporating from the tungsten coil a charge of 0.603 grams of the spinal commonly known as spinel which is a magnesium aluminate Mg0-Al203 composed of a molecule of magnesium oxide and a molecule or" aluminum oxide. This metallic oxide composition or compound like the other spinels or metallic aluminates such as those of calcium or zinc contains or ineludes aluminum oxide in its composition A glow discharge cleaning of the glass plates was first carried out before the actual evaporation of low reflection coatings upon the glass sheets and useful as the directly formed spinel coated sheets as partially transparent mirrors of very good durability and weather resistance.

In Examples 7 and 8 the coatings were or" a thickness of 3 quarter wave length factors with respect to light of 6000 Angstrom units and the mirrors were colored as viewed by the reflections therein.

Further treatment of Example 8 at a higher temperature in the oven and for a longer time resulted in further decreases in the light absorption to less than 1% of the coated glass as some further oxidation was secured. However, the

above products were substantially coatings upon the glass of the desired spinel. In other similar runs other spinels such as calcium aluminate were distilled by thermal evaporation within a vacuum upon glass sheets and the coated glasses were thereafter heated in an electric oven at approximately 400 centigrade in air to reduce the light absorption of such coating and to reform the desired spinel in the coating.

EXAMPLES 9 TO 11 In three separate thermal evaporations carried out at different times sheets of glass, sheetsof silica and a shaped ceramic bowl were given coattings of hard durable aluminum trioxide by the upwards evaporation of aluminum oxide compositions or compounds from a tungsten boat heated by electrical resistance within a vacuum chamber. The compounds employed were in each case inherently capable of being reactively decomposed to aluminum oxide when heated such as the hydroxide, nitrate, formate, acetate or lactate of aluminum. Thus the glasssheets were coated with aluminum oxides by thermally evaporating from the heated boat in the vacuum aluminum acetate Al(C2I-I3O2)3 which decomposed in the vacuum under the heating into aluminum oxides. The coated glass sheets were then oxidized by heatingthe same in anair furnace at 100 centigrade for a week with resultant decrease in the light absorption of the coating as it became oxidized. Aluminum nitrate Al(NO3)3 was used in the coatin of the sheets of the silica with aluminum trioxide by applying the compound to the tungsten boat as a support which was thereafter heated in the vacuum causing decomposi- V 12 varyin distances as hereafter shown'from the evaporation source which was a tungsten filament. Into the latter there was placed some antimony trioxide with the object of forming upon the glass sheets a coating of antimony tetraoxide, a higher oxide of antimony. After the vacuum chamber was closed the glass sheets were cleaned by a glow discharge treatment and the antimony oxide was then thermally evaporated at 10* to 10- millimeters at a low red heat. However, oxygen seems to be lost from the antimony trioxide upon such thermal evaporation within a vacuum as the deposits upon the glass are quite light absorptive, as will be seen in the following table. Sufficient of the antimony trioxide was evaporated such that the heaviest coatin secured was, after a further oxidation treatment by heating the coated glasses for one hour in an air furnace at 425 centigrade, of a thickness of about one-quarter of a wave length of visible light of 5700 Angstrom units or approxtion of the nitrate to aluminum oxide which was then thermally evaporated by raising the temperature of the boat to a further degree. The coat perature of the boat to a high temperature. The 4 coated bowl was then placed in a chamber through which heated oxygen at 200 centigrade was passed for several hours to oxidize the coatings and to permit the securing thereon of a hard durable protective coating of aluminum trioxide primarily which was then durable, weather resistant and reflective.

EXAMPLES 12 TO 16 Within a high vacuum chamber there were placed five pieces of clean glass having a smooth polished surface, the pieces being arranged at imately .070 micron thick. After such an oxidation treatment the light absorption of the coated glasses was negligible. When antimony oxides are heated in air a pentaoxide is formed if the heating is below 380 centigrade and above this temperature and up to 930 centigrade antimony tetraoxide is stable and formed. Thus any of the antimony trioxide or any other lower oxide of antimony present in the coating formed in the thermal evaporation was by the oxidation at 425 centigrade substantially oxidized into the more highly oxidized stable solid antimony tetraoxide. The latter substance has a refractive index of 2.00 whereas antimony trioxide has a higher refractive index of 2.08 to 2.35 and in line with the oxidation of the coating forming the lower index material it will be noticed that the reflection'of the coated article decreases gener-' ally atthese thicknesses as would be expected with a decrease in the refractive index. It is apparent that if I had desired to form a coating Iof antimony pentaoxide instead of one of anti- :mony tetraoxide I would oxidize the thermally deposited coating in contact with air or oxygen at an elevated temperature below 380 centigrade. The coated glass article produced as Example 16 showed a pale yellow color by reflection and a pale blue color by transmission thereby indicatin the approximate thickness of coating indicated and also showing that since such color by reflection was an interference color that the article could be used in the forming of a colored mirror. As such it and the other coat- -ed glass articles so produced are directly useful as partially transparent first or second surface mirrors, as the coatings were very hard and durable. Likewise, for example, there may be placed upon the filament, boat or other evaporation support a salt of antimony such as the sulfate or tartrate which will when heated in the vacuum decompose to provide antimony oxide.

Antimony oxide coated glass sheets Coating Per Cent Per Cent Per Cent Second Examg g gg Thick- Oxidation Light First Sur- Light Surface ple No. Inches ness, Step Transface Re- Absorp- Mirror MIOIOHS mission flection tion Reflection 12 20 None 66 28 6 20 20 .026 Oxidized 86 14 0 l3 5 12 17.3 None as as 7 26' 17. 3 035 Oxidized 81 19 0 18 14 16. 8 None 53 37 10 28 15.8 .042 Oxidized 77.5 22.5 0 215 15 14.1 None so as 12 28' 14.1 .0525 Oxidized 25 0 23 9 1e 12. 25 None.. 48 34 1s 18' 12. 25 070 Oxidized 75. 5 24. 5 0 23. 7

EXAMPLE 17 A clean glass plate was placed in a vacuum chamber and thereupon cleaned further by an oxygen lost during the thermal evaporation of the higher tungsten trioxide in the vacuum was again supplied to the coating by the oxidation in air to form in the coating tungsten trioxide.

electric glow discharge. After this there was In order to further bring out the changes thermally evaporated from a tungsten filament brought about by the several steps, a second simin a go d vacuum some stanni de r tin ilar run with three other pieces of glass was made oxide and a deposit secured upon the glass plateapplying the same amount of the tungsten tri- When the coated glass plate was removed from oxide, however, directly upon the similarly placed the vacuum chamber and measured for light glass sheets and omitting the aluminum coating. transmission it showed 78% light transmission. Thus tungsten oxide coatings of a light to a deep It also had a first surface reflectivity of and blue shade were directly formed upon the glass thereby had a light absorption of 2%. When this and clearly contained some of the lower tungsten coated plate was then heated in an oven at 500 oxide or was primarily'iormed of the blue oxide. centigrade the front surface reflection remained 5 After making optical measurements upon these the same but the light transmission increased to glasses they were heated in the oven in a similar 79% and the light absorption decreased to 1%. manner at 250 centigrade to oxidize the coatings Thus oxidation changed the optical properties of whichlost all blue color and became a faint yel the coating upon the glass ndi in an oxidation low only by light transmission. The change in to v t n P d by vi a c a 20 the measured values with respect to the reflection, upon the glass which was substantially the higher transmission overall of white light, and absorption tin dioxide. appears in the following table.

Tungsten oxide coated glass sheets Exi'tqinple g lgg Oxg'gation jigfi 2 1 145 11 1? t f g g t Inches Microns ep g g Absorption 21 20 None 7s 21 1 20 .070 Oxidized vs 23.5 0 22 14 'one. 77 9.5 13.5

.141 Oxidized s7 11 2 3 10 None 62 10 28 10 .282 Oxidized. 84 1s 3 EXAMPLES 18 TO 23 EXAMPLE 24 Surface mlrror? 9 alummum m Some ferric oxide F8203, the ferric trioxide, coating of tungsten trioxide on the face of the 40 which is of a brown color was thermally evapc alummum were made by placmg three clean rated from a tungsten filament or a tantalum Smooth fsurface mates of glass in a vawum cham' boat which was heated in a high vacuum upon at dlfieren? dlstances away mm the two tunga piece of previously well cleaned glass. Oxygen sten evaporation filaments therein. One of the was lost as indicated by the vacuum gauges filaments was loaded with a considerable amount tached to the chamber and the deposit upon the of alummum and m w Second filament was 5 sheet of glass was of a greenish brownish grey P15310961 gram of the hght yellow tungsten color when looked at through the coated glass. After the chamber was closed the glass The coated glass showed a first surface reflection plates were cleaned further by an electric glow of 29% a Second urfa reflectio f 24%, a dISPharge preferably although thls mlght be light transmission of 28%, and a light absorption omitted, and then the vacuum was reduced 5 of 43%. The deposit appears to be a mixture of low 10 3 mllllmeters and the alummum was ther' iron oxides in which ferrous oxide predominates mally evaporated in a sufiicient amount to give an as upon heating the coated glass f 4 hours at opaque reflective mirror coating of aluminum on 4 Centigrade the heavy light absorption all of the glass plates. After the aluminum evapocreased to 12%. Thepthus oxidized coating would mtlon was stopped the filament containing the 5 seem to be substantially composed of ferric tritungsten trioxide was heated by passing an elec- Y Oxida trio current through the filament and as the tungsten trioxide evaporated the vacuum gauges XA L 25 attached to the chamber indicated the liberation from the metallic oxide of a gas which was oxy- Upon a clean piece of sheet glass there was en. When the coated mirrors were removed depisited in a high uum by thermal evaporaf om the Vacuum chamber the mirrors had a tion of 0.5 gram of the dark green chromium general strong blue color and when these mirrors sesquioxifie (@203) a coating of a dark naturewere then heated in an oven in air at 250 centi- T coaiimg was red brown shade by trans grade fo 5 minutes to 30 minutes, which did not mitted light and the coated glass showed a first alter the aluminum coating, the blue color dis- Surface reflection of 12% and light transmis appeared and was replaced by a fi ht yellow sion of 31%. Thus 57% of the incident light was dominant shade. With these stronger coloring-:s absorbed in the Coating. After heating in air in the tungsten oxide coatings due to selective in a furnace held at Centigrade or n hou colored light absorption other less prominent inthe coating of mixed chromium oxides was terference colors were also evident by reflection. Stantially Converted to c m m s squ o d a The blue color is characteristic of the lower oxide the first surface reflection h d to 14%. th of tungsten known as the blue oxide and reported li ht tran mi sio c a d o 6 and the to be W308 or a lower oxide than the yellow light bs rpti n d creased her by to 22%. T tungsten trioxide W03. It is apparent that the heated coatings were extremely hard. The unheated deposit and the heated oxidized coating each also showed light interference color in the reflected light from their surfaces and the color was found to shift spectrally in the heating process in a manner which indicated that the refractive index of the coating was also decreasing. The final coating of chromium sesquioxide produced in this manner was of the order of .188 micron thickness.

EXAMPLE 26 In the preparation of Example 25 there was also placed in the vacuum chamber at 12 inches from the filament an aluminum coated glass mirror so that it would also receive the chromium oxide deposit formed during the evaporation. The mirror coated side was placed facing the fllament and the glass was inclined at a slight angle thereto so that the opposite ends of the face were slightly closer or slightly further away from the filament than the 12 inches true for the center of the mirror. When the coated mirror was removed from the vacuum chamber one end had a reflection of 18% and was a green yellow mirror, the center had a reflection of 14% and was a green mirror, and the other end was a red mirror of 21% reflectivity. After heating the coated mirror in air at 250 centigrade for 15 to 30 minutes which did not affect the aluminum layer the respective ends'were found to have their light reflectivities increased to 48%, 49% and 58% thus clearly indicating that a decrease in light absorption by the coating had occurred during the heating and oxidation as more light was then able to traverse the coating and be reflected from the backing aluminum layer. The colors in the mirrors were developed by light interference and shifted slightly when the deposit was heated and oxidized.

EXAMPLES 27 AND 28 Chromium sesquioxide in the same 0.5 gram amount was placed in a tungsten filament and thermally evaporated out of such heated filament in a high vacuum of the order of l millimeters upon two mirror coated pieces of glass placed at a distance of 22 inches from the filament. One piece of glass had previously been coated by thermal evaporation with an opaque mirror reflective layer of aluminum of about 89% reflectivity and the other piece had in a similar manner been coated with a chromium metal reflective layer of approximately 55% reflectivity. The coating of chromium oxides was deposited in each case directly upon the mirror reflective metal carried by the glass support and when each was removed from the vacuum chamber two entirely different mirrors were found to have been produced. The coated aluminum article was a mirror of front surface reflectivity of 36% and of a pure deep gold color while the coated chromium article was a mirror of front surface reflectivity of 5% of a deep red blue color. These mirrors were then heated as in Example 26 at 250 centigrade for a sufilcient length of time to produce oxidation in the coatings such as 30 minutes without affecting the mirror metal coatings under the chromium oxide deposits. This resulted in an aluminum-chromium sesquioxide coated mirror having a reflectivity of 42% and a much deeper gold color and a chromium-chromium sequioxide coated mirror reflecting a pure blue color with 5% reflectivity. The mirrors were in each case quite hard and durable.

16 EXAMPLE 29 In the evaporation of th chromium sesquioxide in Examples 25, 26, 27 and 28 from the hot tungsten filament within the vacuum oxygen was lost from the chromium oxide as shown by a surge of gas registered at the start of the evaporation and thereafter by the vacuum gauges attached to the chamber. When the tungsten filaments were removed from the chamber after the deposition it was found that the tungsten filaments had been partially attacked and eaten away by the liberated oxygen acting upon the hot tungsten to form tungsten oxides which then evaporated with the chromium oxides. Thus, the deposits secured in the thermal evaporation also contained tungsten oxidesmixed with the chromium oxides, each metallic oxide being of a lower state of oxidation. When the deposits were thereafter oxidized by heating the coated articles in air at elevated temperatures the mixed chromium and tungsten oxides each oxidized to the more highly oxidized chromium sesquioxide and tungsten trioxide as shown above and in Examples 18 to 23. In a similar manner if the chromium oxide is evaporated from a tantalum heated support or filament the oxygen liberated by the chromium sesquioxide when heated in the vacuum reacts to a considerable degree with the hot tantalum and there is deposited upon the article a mixture of chromium and tantalum oxides including the lower oxides of these metals and when such deposits are then heated in an oxygen containing atmosphere such as in air at 250 centigrade the various oxides are oxidized to chromium sesquioxide and tantalum pentaoxide. While such attack upon tungsten during the evaporation of chromium sesquioxide is negligible leading to very slight contamination in the deposit the attack upon tantalum is very considerable.

By way of further example of the use of the invention in the distillation of mixtures of metallic oxides there was applied to a tungsten filament a mixture of equal amounts of chromium sesquioxide and tantalum pentaoxide and these were thermally evaporated from the filament when it was heated to a high temperature in the vacuum. The deposit received upon a glass plate was then oxidized by heating the same at 500 centigrade for one hour which resulted in the reflection of the coated plate changing and the light absorption of the plate decreasing.

EXAMPLES 30 AND 31 By way of making a hard surface aluminum mirror article of high reflectivity which carried a layer of the hard chromium sesquioxide as a protective coating thereon there was placed in a vacuum chamber two aluminum opaque mirrors of approximately 89% reflectivity with the aluminum faces toward the tungsten evaporation element. Into the latter there was placed 0.050 gram of chromium sesquioxide and the mirrors were positioned at a distance of 15.5 and 22 inches away therefrom. The chamber was then closed and evacuated to a good vacuum and the tungsten evaporating element was then raised to a high heat and the chromium oxides evaporated and deposited upon the aluminum surfaces. After removing these coated mirrors from the vacuum chamber the one placed-at 15.5 inches had a reflection value of 67% and that placed at 22 inches had a reflection of 82%. These coated glasses werethen heatedat 250 centigrade for 30 minutes and the reflectivities in each case EXAIVIPLES 32 TO 34 Zirconium dioxide pieces weighing .110 gram were evaporated from a tungsten filament in a tances away from the same as shown in the following table. Each piece of glass thus received a coating of somewhat different thickness from the other pieces and when the evaporation had been completed and the glasses were removed from the coating chamber each was found to show different reflectivities and light transmission values. These are shown in the following table as well as the degree of light absorption by the coated glasses. The light absorption was found to increase with the thicker coatings as expected and the presence of titanium oxides of lower oxidation state than titanium dioxide was thereby indicated as the coatings were othervacuum of 10* millimeters upon three pieces of previously cleaned flat glass placed at different 3 fit i 9 m have any distances away from the filament as shown in e a 1c 00 e g asses i the following table. Optical measurements were each heated at 450 centzgrade in contact with made upon the coated pieces as they were rean for 15 mmutes found that 51.1011 moved from the chamber and again after the treatment completely eiminated the absorption deposits upon the glass supports had been heated of f' m the coated art1c1 S- Thus the in an electric furnace in air at 540 centigrade for absorbm? lower oxldes of mu Present m two hours. This brought about a decrease in the the deposlt were completely OXldlZed and conlight absorption of the coated glasses as the Verted by the heatmg mm the hlghly OXldlZed coating was oxidized t some degree to give a colorless titanium dioxide which then formed coating which was free of the lower oxides subthe coatmgs- The coated glasses were as Shown stantially and composed in the main of sh in the table directly useful as either first or sired colorless zirconium dioxide. The coatings Second Surface partially t p ent mirrors. were very hard and the optical data was as fol- For such uses the coatings are quite a act v lows: as they are very hard and durable. The coat- P o t P 0 t mxa'gnple 1532 3352, T fc i i s, Oxidation eifighetn grolftn 'if gf Inches Microns Step igififg Absorption s2 11 None 80 18.5 1.5

11 0xidizcd.. s3 17 0 33 8 None 74 24.5 1.5

a Oxidized" 7s. 5 21. 5 0 34 6 None 78 20.5 1.5

6 Oxidized 79 21 0 Each of the coated articles thus produced was ings may also be used when further coatings are of u e c y as a p r ly transparent m r r applied thereto as a layer in a low reflection of good durability. coating for the forming of high light transmis- In Example the coatmg 3 H Wave sion glass. Obviously the unheated deposits motors thlck 'wlth respect I f f of 4500 besides being of undesired refractive index are fiii g t fi' g is i also very poorly suited for use in such high f g i i igg z ;i %g transmission coatings in view of their own peg g i y g e e e culiar high light absorbing properties.

The coating thickness of Examples 36 and 38 EXAMPLES 36, 37 AND 38 5 were approximately one quarter and one half a From a small tungsten coil wound in tubular Wave factor in thickness W p c t 5500 shape there was evaporated in a vacuum cham- Angstrom un s yell w light- Per Cent o t P o t P o t P o 1; Examgfig riiic if Oxidation l igh Fl r st 1 1 1 iglft 232%; pic No 5 h 2 ness, Step Transface Re- Absorp Mi C e Micrcns mission fiection tion l 35 None... 63 26. 5 10.5 Oxidized. 73 27 0 2s. 5 3e -1 None... 62 27.5 10.5

Oxidized. 72 2s 0 27 37 None.... 28 12 Oxidized. 72 28 0 27. 5 38 None... 60 10 30 Oxidized. 00 10 0 10 her at a vacuum of 10' millimeters small pieces of titanium dioxide loaded thereon Which weighed 0.465 gram total. A deposit of titanium oxide material which included some of the lower oxides of titanium as well as titanium dioxide was formed upon four pieces of previously cleaned glass placed in the vacuum chamber facing the filament and located at various dis- 75 away from the evaporation source.

EXAMPLES 39, 40 AND 41 In a similar manner 0.133 gram of titanium dioxide was thermally evaporated from a tungsten filament in a vacuum of 10 millimeters and deposited upon three pieces of clean glass placed in the chamber at various distances When the pieces of glass carrying the deposit thereon of titanium oxide material were measured for reflection, transmission and light absorption the results were as shown in the next table for the three coated glasses. The light absorption present in each case was removed and the deposit oxidized when the'deposits were directly flamed with a Bunsen burner flame for 15 minutes. The changes in the optical properties of the coatings as against the non-oxidized or non-flamed deposits are quite striking as is readily apparent from the table of results. Each of the coated articles thus made was of direct use as a mirror of partially transparent nature.

In the foregoing general description and specific examples, it will be observed that the method comprises the initial step of depositing upon a surface by thermal evaporation in alvacuum a coating which includes lower oxides of metals capable of forming oxides of several oxidation states. The thermal evaporation step involves the use of a metallic oxide as the material evaporated. This material may be of high or low oxidation state, or a mixture of different oxides or a spinel, all of which are included within the term metallic oxide as used herein. Alternatively the starting material may be a metallic compound which decomposes to form an Per Cent Per Cent Example 152%., Titlin agate r gggg, 5.53"

Inches Microns ep s Reflection Absorption 39 20 None 84 1 016 Oxidized. 85. 5 14. 5 0 4O 17. 3 None 80 17. 5 2. 5

17. 3 O24 OXidized 82 18 0 41 14.1 None 70.5 23 6.5

14.1 032 OXidized 76 2'1 0 EXAMPLES 42 AND 43 oxide when heated. In order to improve the A small quantity of manganese dioxide M1102 was placed in a tungsten filament and thermally evaporated in a high vacuum of the order of 10- As the oxide was heated and thermally evaporated it lost oxygen as indicated by the vacuum gauges as was also evident in a similar manner when the titanium dioxide was thermally evaporated in the above examples. Two smooth pieces of plate glass were used during the evaporation as supports upon which the manganese oxide material was deposited, the pieces being placed at different distances away from the filament such that one received twice the thickness of coating that was formed upon the other. The deposits formed were highly absorptive but did not appear metallic in any way and were formed of a mixture of manganese oxides including the lower oxides which are highly light absorptive. After making measurements of the reflection and light transmission of the glasses carrying the deposits these coated glasses were heated for minutes in air at 450 centigrade in an electric furnace for the purpose of oxidizing the deposit and forming the higher oxides of manganese from the lower oxides present in the deposit. Such heating converted the coating into a coating which was substantially manganous manganic oxide M11304. The light absorption was decreased by such heating and oxidation but as the oxide produced, manganous manganic oxide, is still a somewhat dark colored material absorption of some light by the coating produced would be expected. The measurements of the light absorption and other values appear as follows. The thinner coating is of a quarter wave length thickness and the thicker coating is of a half wave length thickness of yellow light.

physical properties of this film, and particularly its light transmission properties, at least some of the lower oxides present as a result of the thermal evaporation are oxidized to a higher oxide.

Since the improved physical properties of the film are to be retained under normal pressure and temperature conditions, the higher oxides formed are stable under these conditions. Therefore, the essential requirement is that the oxidation of the deposited film shall be carried out under conditions of temperature and pressure, dependent upon the particular atmosphere employed, such that the desired higher oxides are formed, the higher oxides thus formed being stable under these temperature and pressure conditions as well as under normal pressure and temperature conditions.

In order to convey a thorough understanding of the present invention to those skilled in the art, the foregoing specific examples have been included together with results of actual tests and measurements accomplished thereon. It is to be understood, however, that these specific examples are set forth for the purpose of assisting in the practice of the invention and are in no sense to be considered as limiting the scope of the appended claims.

What I claim as my invention is:

l. The method of forming on the surface of an article a continuous coating composed substantially completely of a highly oxidized solid metal lic oxide having the relatively high light transmission characteristics normal to such highly oxidized solid metallic oxide, comprising providing on a heat radiating support body a metallic oxide of a metal capable of forming oxides of a plurality of different oxidation states, the metal beingselected from the group consisting of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten and manganese, heating the support body adjacent the surface of the article in a vacuum and thereby heating the metallic oxide to evaporate metallic oxide and deposit upon the surface a continuous'and light absorbing metallic oxide coating comprising a metallic oxide of lower oxidation state and higher light absorption than that of the said. highly oxidized solid metallic oxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to said highly oxidized state, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atn-iosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees Centigrade sufiicient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

2. The method of forming on the surface of an article a continuous coating composed substantially completely of a highly oxidized solid metallic oxide having the relatively high light transmission characteristics normal to such highly oxidized solid metallic oxide, comprising providing on a heat radiating support body a metallic oxide of a metal capable of forming oxides of a plurality of different oxidation states, the metal being selected from the group consisting of aluminum titanium. chromium, tin, zirconium, antimony, iron, tantalum, tungsten and manganese, heating the support body adjacent the surface of the article in a vacuum and thereby heating the metallic oxide to evaporate metallic oxide and deposit upon the surface a continuous and light absorbing metallic oxide coating comprising a metallic oxide of lower oxidation state and higher light absorption than that of the said highly oxidized solid metallic oxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to said highly oxidized state, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere of air at atmospheric pressure, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade suflicient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

The method of forming on the surface of an article a continuous coating composed substantially completely of a highly oxidized solid metallic oxide having the relatively high light transmission characteristics normal to such highly oxidized solid metallic oxide, comprising providing on a heat radiating support body a compound of oxygen and metals, one of the metals being capable of forming oxides of a plurality of different oxidation states, the metal being selected rom the group consisting of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten and manganese, heating the sup port body adjacent the surface of the article in a vacuum and thereby heating the metallic oxide to evaporate metallic oxide and deposit upon the surface a continuous and light absorbing metallic oxide coating comprising a metallic oxide of lower oxidation state and higher light absorption than that of the said highly oxidized solid metallic oxide, terminating deposition of said coating before said coating attains thickness which would render the coating opaque when substantially completely oxidized to said highly oxidized state,

and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidiz ing the oxide of lower oxidation state by subject ing the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above ZOOdegrees centigrade suflicient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

4. The method of forming on a support surface a continuous coating composed substantially completely of aluminum trioxide having the rela-- tively high light transmission characteristics .of aluminum trioxide, comprising providing on a heat radiating support body an oxide of aluminum, heating the support body adjacent the support surface in a vacuum to evaporate and deposit upon the support surface a continuous and light absorbing aluminum oxide coating including an aluminum oxide of lower oxidation state than aluminum trioxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to aluminum trioxide, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50' mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufiicient to oxidize the oxide of lower oxi dation state to form a coating composed substantially completely of aluminum trioxide.

5. The method of forming on a support surface a continuous coating composed substantially completely of aluminum trioxide having the relatively high light transmission characteristics of aluminum trioxide, comprising providing on a heat radiating support body aluminum trioxide, heating the support body adjacent the support surface in a vacuum to evaporate and deposit upon the support surface a continuous and light absorbing aluminum oxide coating including an aluminum oxide of lower oxidation statethan aluminum trioxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to aluminum trioxide, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade suflicient to oxidize the oxide of lower oxidation state to form a coating composed substantially completely of aluminum trioxide.

6. The method of forming on a support surface a coating composed substantially completely of a highly oxidized solid metallic oxide having relatively high light transmission characteristics normal to such highly oxidized solid metallic oxide, comprising providing on a heat radiating support body a compound of oxygen and metals, one of the metals being aluminum, heating the support body adjacent the support surface in a vacuum and thereby heating the compound-to evaporate and deposit upon the support surface a continuous and light absorbing metallic oxide coating comprising an aluminum oxide of lower oxidation state than aluminum trioxide, termi nating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 5.0 mm. of mercury, and while subjecting said coating to said atmosphereheating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the particular'oxide of lower oxidation state to form a coating composed sub stantially completely of said highly oxidized solid metallic oxide.

7. The method of forming on a support surface a continuous coating composed substantially completely of chromium sesquioxide having the relatively high light transmission characteristic of chromium sesquioxide, comprising providing on a heat radiatin support body an oxide of chromium, heating the support body adjacent the support surface in a vacuum to evaporate and deposit upon the support surface a continuous and light absorbing chromium oxide coating including a chromium oxide of lower oxidation state than chromium sesquioxide, terminating deposition of said coating before said coating attains a thickness which would render the coatin opaque when substantially completely oxidized to chromium sesquioxide, and thereafter altering the optical properties of said coating to increase its light'transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the oxide of lower oxidation state to form a coating composed substantially completely of chromium sesquioxide.

8. The method of forming on a supportsun face a continuous coating composed substantially completely of titanium dioxide having the relatively high light transmission characteristics of titanium dioxide, comprising providing on a heat radiating support body an oxide of titanium, heatingthe support body adjacent the support surface in a vacuum to evaporate and deposit upon the support surface a continuous and light absorbing titanium oxide coating includin a titanium oxide of lower oxidation state than titanium dioxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to titanium dioxide, thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient tooxidize the oxide of lower oxidation state to form a coatingwcomposed substantially completely of tita-' nium dioxide.

9. The method of forming on a support surface a continuous coating composed substantially completely of aluminum trioxide having the relatively high light transmission characteristic of aluminum trioxide, comprising providing on a heat radiating support body an oxygen containing compound of aluminum, said compound being inherently reactive upon heating to decompose to form aluminum oxide, heating the support body adjacent the support surface in a vacuum and thereby heating the compound to decompose the compound to form aluminum oxide and to evaporate and deposit upon the support surface a continuous and light absorbing aluminum oxide coating including an aluminum oxide 'of lower oxidation state than aluminum trioxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to aluminum trioxidc, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the oxide of lower oxidation state to form a coating composed substantially completely of aluminum trioxide.

10. The method of forming on a support surface a continuous coating composed substantially completely of antimony tetraoxide having the relatively high light transmission characteristic of antimony tetraoxide, comprising providing on a heat radiating support body an oxygen containing compound of antimony, said compound being inherently reactive upon heating to' decompose to form antimony oxide, heating the support body adjacent the support surface in a vacuum and thereby heating the compound to decompose the compound to form antimony oxide and to evaporate and deposit upon the surface a continuous and light absorbing antimony oxide coating including an antimony oxide of lower oxidation state than antimony tetraoxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to antimony tetraoxide, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the oxide of lower oxidation state to form a coating composed substantially completely of antimony tetraoxide.

11. In the method of making mirrors, the

deposition on a reflective mirror coating of a consisting ofaluminum, titanium, chromium,

tin, zirconium, antimony, iron, tantalum, tungsten, and manganese, heat-ing the support body adjacent the mirror coating in a vacuum and thereby heating the metallic oxide to evaporate and deposit upon the mirror coating a continuous and light absorbing metallic oxide coating in cluding a metallic oxide of lower oxidation state than that of the said highly oxidized metallic coating, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substan-' tially completely oxidized to said highly oxidized state, thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the particular oxide of lower oxidation state to form a coating composed substa'n tially completely of said highly oxidized solid metallic oxide.

12'. The method of making transparent mirrors by applying to a smooth surface of a transparent support a continuous coating composed substantially completely of a highly oxidized solid metallic oxide having the relatively high light transmission characteristics normal to such highly oxidized solid metallic oxide, comprising providing on a heat radiating support body a metallic oxide of a metal capable of forming oxides of several different oxidation states, the

metal being selected from the group consisting of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten, and manganese, heating the support body adjacent the smooth surface in a vacuum and thereby heating the metallic oxide to evaporate and deposit upon the support surface a continuous and light absorbing metallic oxide coating including a metallic oxide of lower oxidation state than that of the said highly oxidized metallic oxide, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to said highly oxidized state, and thereafter altering the optical properties of said coating to increase its light transmission characteris tics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

13. The method of forming on a support sur face a continuous coating composed substantially completely of a highly oxidized solid metallic oxide having the relatively high light transmission characteristics normal to such highly oxidized solid metallic oxide, which comprises depositing on said surface by thermal desposition in a vacuum a uniform continuous coating of metallic oxide, the metal of said oxide being selected from the group consisting of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten and manganese, and being capable of forming oxides of several oxidation states, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when sub' stantially completely oxidized to said highly oxidized state, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and While subjecting said coating to said atmosphere heating said coat ingto a temperature above 200 degrees centigrade sufficient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

1-4. The method of forming on a support surface a continuous coating composed substantially completely of a highly oxidized solid metallic oxide having the relati ely high light transmis sion characteristics of the highly oxidized solid metallic oxide, which comprises depositing on said surface by thermal deposition in a vacuum a uniform continuous coating of metallic oxide, the metal of said oxide being selected from the group consisting of aluminum, titanium, chro mil-1m, tin,- zir'conium, antimony, iron, tantalum, tungsten and manganese, and being capable of forming oxides of several oxidation states, the coating including a metallic oxide of lower oxidation state than that of the desired coating, terminating deposition or" said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to said highly oxidized state, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sumcient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

15. The method of forming on a support surface of a transparent body a highly transparent continuous coating composed substantially completely of a highly oxidized solid metallic oxide having the relatively high light transmission characteristics of the highly oxidized solid metallic oxide, which comprises depositing on said surface by thermal deposition in a vacuum a uniform continuous coating of metallic oxide, the metal of said oxide being selected from the group consisting of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten and manganese, and being capable of forming oxides of several oxidation states, the coating including a metallic oxide of lower oxidation state than that of the desired coating, terminating deposition of said coating before said coating attains a thickness which would render the coating opaque when substantially completely oxidized to said highly oxidized state, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least 50 mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufiicient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

16. The method of forming on a support surface a continuous coating efiective to produce color by light ray interference and composed substantially completely of a highly oxidized solid metallic oxide having the relatively high light transmission characteristics of the highly oxidized solid metallic oxide, comprising providing on a heat radiating support body a metallic oxide of a metal capable of forming oxides of several different oxidation states, the metal being selected from the group consisting of aluminum, titanium, chromium, tin, zirconium, antimony, iron, tantalum, tungsten and manganese, heat" ing the support body adjacent the support surface in a vacuum and thereby heating the metallic oxide to evaporate and deposit upon the support surface a continuous and light absorbing metallic oxide coating including a metallic oxide of lower oxidation state than that of the desired coating, terminating the deposition of said coating when it has a thickness which when it is substantially completely oxidized to its highly oxidized state represents an odd integral number of quarter wave length factors of visible light of a predetermined wave length and remains 28 partially transparent to produce color by light interference of light of the predetermined wave length, and thereafter altering the optical properties of said coating to increase its light transmission characteristics by substantially completely oxidizing the oxide of lower oxidation state by subjecting the coating to an atmosphere having a partial pressure of oxygen of at least mm. of mercury, and while subjecting said coating to said atmosphere heating said coating to a temperature above 200 degrees centigrade sufficient to oxidize the particular oxide of lower oxidation state to form a coating composed substantially completely of said highly oxidized solid metallic oxide.

ARTHUR R. WEINRICH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,118,795 Littleton May 24, 1938 2,281,474 Cartwright Apr. 28, 1942 2,366,516 Geffcken et al Jan. 2, 1945 2,456,899 Strong Dec. 21, 1943 FOREIGN PATENTS Number Country Date 504,620 Great Britain Apr. 25, 1939 

1. THE METHOD OF FORMING ON THE SURFACE OF AN ARTICLE A CONTINUOUS COATING COMPOSED SUBSTANTIALLY COMPLETELY OF A HIGHLY OXIDIZED SOLID METALLIC OXIDE HAVING THE RELATIVELY HIGH LIGHT TRANSMISSION CHARACTERISTICS NORMAL TO SUCH HIGHLY OXIDIZED SOLID METALLIC OXIDE, COMPRISING PROVIDING ON A HEAT RADIATING SUPPORT BODY A METALLIC OXIDE OF A METAL CAPABLE OF FORMING OXIDES OF A PLURALITY OF DIFFERENT OXIDATION STATES, THE METAL BEING SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, TITANIUM, CHROMIUM, TIN, ZIRCONIUM, ANTIMONY, IRON, TANTALUM, TUNGSTEN AND MANGANESE, HEATING THE SUPPORT BODY ADJACENT THE SURFACE OF THE ARTICLE IN A VACUUM AND THEREBY HEATING THE METALLIC OXIDE TO EVAPORATE METALLIC OXIDE AND DEPOSIT UPON THE SURFACE A CONTINUOUS AND LIGHT ABSORBING METALLIC OXIDE COATING COMPRISING A METALLIC OXIDE OF LOWER OXIDATION STATE AND HIGHER LIGHT ABSORPTION THAN THAT OF THE SAID HIGHLY OXIDIZED SOLID METALLIC OXIDE, TERMINATING DEPOSITION OF SAID COATING BEFORE SAID COATING ATTAINS A THICKNESS WHICH WOULD RENDER THE COATING OPAQUE WHEN SUBSTANTIALLY COMPLETELY OXIDIZED TO SAID HIGHLY OXIDIZED STATE, AND THEREAFTER ALTERING THE OPTICAL PROPERTIES OF SAID COATING TO INCREASE ITS LIGHT TRANSMISSION CHARACTERISTICS BY SUBSTANTIALLY COMPLETELY OXIDIZING THE OXIDE OF LOWER OXIDATION STATE BY SUBJECTING THE COATING TO AN ATMOSPHERE HAVING A PARTIAL PRESSURE OF OXYGEN OF AT LEAST 50 MM. OF MERCURY, AND WHILE SUBJECTING SAID COATING TO SAID ATMOSPHERE HEATING SAID COATING TO A TEMPERATURE ABOVE 200 DEGREES CENTIGRADE SUFFICIENT TO OXIDIZE THE PARTICULAR OXIDE OF LOWER OXIDATION STATE TO FORM A COATING COMPOSED SUBSTANTIALLY COMPLETELY OF SAID HIGHLY OXIDIZED SOLID METALLIC OXIDE. 